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cleaning fiberglass shower stall

I have a fiberglass shower stall and plexiglass shower doors. They are very hard to clean due to water deposits. We have a well but our water is not brutally hard. Nonetheless, we've tried many over-the-counter cleaning products many of which claim to be specifically for removing water deposits. Some of them work better than others but it's still a real struggle!

Can you recommend a product which may really work!!?? Also, is it okay to use a scotchbrite pad to clean the surfaces? I've always used a soft bristle scrub brush and rag.


Skippack, PA

Re: cleaning fiberglass shower stall


Don't use a green scrubbie as that will scratch the surface, making it more porous than before.

When I owned a 1-piece tub unit my favorite was CLR. Granted, after cleaning the shower I needed new lungs, but after letting the spray set for a spell, the nausea to go away and my eyes to stop watering, it wiped clean right quick. Zep makes a very similar product available at Home Burrito in gallon containers much cheaper than the spray bottles of CLR from the Piggly Wiggly, and they have decent face masks with charcoal filters in the tool section.

Re: cleaning fiberglass shower stall


No, use a WHITE Scotchbrite pad to clean your fiberglass, not a green one. All Scotchbrite pads except the white ones have an abrasive impregnated into the plastic fiber they're made of. The white Scotchbrite pads don't have any abrasive in the fiber. You can get much larger scotchbrite pads (from white to black) at any Janitorial Supply Store. Just ask for a white "Doodle Bug Pad".

Four ideas:
1. The reason why phosphoric acid is the active ingredient in many bathroom cleaners is that it cuts through soap scum like a hot knife through butter, but won't attack chrome, even at high concentrations. Any Janitorial Supply store will also sell phosphoric acid based toilet bowl cleaners which are gelled to stick well to the smooth steep surfaces of your toilet bowl, AND your fiberglass shower walls.

2. If you understand the chemistry, you'll realize that oven cleaner actually causes soap scum to revert back into soap by driving the reaction that converts soap into soap scum in the opposite direction. So, put on some rubber gloves and leave some oven cleaner on your fiberglass tub for a half hour or so for it to work, and it'll be cleaner than a drill sargeant's whistle when you wipe it off. (Oven cleaner shouldn't harm fiberglass, but test a small area first to be on the safe side.)

PS: The following explains the chemistry of soap scum and how best to avoid it's formation in the first place:

3. The reason you're having a rough time with the shower is because the hardness in your water is creating more soap scum than it would if you had soft water.

But, the reason you have soap scum in the first place is because, like everyone else, you're using a bar soap in your bathroom shower.

A soap molecule is nothing more than a fatty acid attached to a sodium or potassium ion, like this:

(aliases: steric acid or "sodium stearate")

The equals sign between the two diagrams indicates that they're just two different ways of drawing the same molecule. The long "hydrocarbon chain" (this business: /\/\/\/\/\/\) combined with a "carboxylic group" ( the -(C=O)-O- thingy) on the end is called a "fatty acid". Vegetable oil molecules each contain three fatty acids. Bar soaps are made from vegetable oils like Palm oil and Olive oil, which is where the Palmolive company got it's name. Bar soap is really nothing more than a hunk of fatty acids with a sodium ion attached to each fatty acid (as shown in the drawing above).

As long as there's a sodium or potassium ion at the end of that fatty acid, then you have a soap molecule and that soap molecule is soluble in water because the sodium (Na+) or potassium (K+) ion is strongly attracted to the polar H2O molecules in water.

But, when you have hard water you have Calcium (Ca++), Magnesium (Mg++) or Iron (Fe+++) ions in your water, and soap scum molecules will form. A soap scum molecule is nothing more than two fatty acids that have connected end-to-end to a common Calcium or Magnesium ion, like this:

(known on the streets as "calcium stearate")


(claims his name is "magnesium stearate")

(and you can imagine three fatty acids connected to a central iron (Fe+++) ion.)

Before, the soap molecule was soluble in water because the sodium or potassium ion on the end of the molecule was highly attracted to polar water molecules.

Now, with two fatty acids attached to a single calcium ion, it's those hydrocarbon chains at each end of the molecule that are sticking out into the water. Now, just like oil and water don't mix, hydrocarbon chains are not attracted to water molecules at all, and that results in soap scum molecules having very much less solubility in water than soap molecules do. That's why soap scum precipitates out of soapy water and collects on the side of your bathtub. So, soap scum is nothing more than soap that's lost it's solubility in water.

By applying oven cleaner, which is sodium hydroxide or NaOH, you greatly increase the number of sodium ions (Na+) in the water, and that drives the chemical reaction that created the soap scum in the opposite direction. That is, in the presence of oven cleaner (or lots and lots and lots of sodium ions), soap scum molecules break back down to soap molecules again. And, of course, soap is much easier to clean up because it's soluble in water.

4. But, you should be aware that you can probably eliminate the formation of soap scum in your bathroom by changing the kind of soap you use:

The difference between a "soap" and a "detergent" is that soap is made from natural products (like Palm and Olive oils), whereas detergents are synthetic soaps. Being synthetic, detergents can be formulated so that they either aren't attracted to the hardness ions in water or don't lose their solubility even if they do react with those hardness ions. That is, the reason you don't have a soap scum ring in your kitchen sink like you do in your bathtub is because you use a dish washing DETERGENT in your kitchen sink, and synthetic detergent molecules can be made to overcome the limitations of natural soap molecules, such as losing their solubility in the presence of hard water.

Fatty acids are also called "lipids", and some people have sensitive skin that breaks out in rashes when it comes into contact with fatty acids. If you go to your local p h a r m a c y, you can buy "lipid-free" skin cleansers like Aquanil or Cetaphil or the one shown below:

Since these skin cleansers don't contain any fatty acids, they shouldn't form a soap scum no matter how hard your water is, and so you should be able to avoid soap scum entirely by using a lipid free skin cleanser in your shower. Certainly, if you use dish washing detergent in your shower, you won't have any more of a problem with soap scum on your shower walls than you do with it in your kitchen sink, but I'd try the lipid free skin cleanser first.

You can learn more than you need or want to know about soaps and detergents at the Soap & Detergent Manufacturer's Association's web site at:


PS: (you don't need to know the rest)

We just call it "soap scum", but those two soap scum molecules shown above are actually called calcium stearate and magnesium stearate, respectively. Both of these chemicals are used as fillers in the p h a r m a c e u t i c a l industry. Every time you swallow a pill, even just a vitamin, you're swallowing some calcium stearate and/or magnesium stearate. More simply put, you're swallowing some "soap scum". But, the bright side is that the soap scum in the pill is of "food grade" purity. :)

Re: cleaning fiberglass shower stall

***...great responses...thank you....good stuff!!

Re: cleaning fiberglass shower stall

I have used a white scotchbrite pad to clean my fiberglass. And I also use a 3m heavy oxidation compound. That keeps my fiberglass well off. Thanks for a post HoustonRemodeler. Great information!

Re: cleaning fiberglass shower stall

Yes, thanks for the great post Houston Remodeler. :)

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